The extraction of DNA from Neanderthal fossils has allowed geneticists to identify the legacy modern humans received from interbreeding with them during the Ice Age. Who would have thought that your risk of smoking depends on whether you inherited particular genes from a long-lost branch of the human family tree?
When modern humans spread out of Africa they found that Neanderthals had populated much of the world first. Enough interbreeding occurred that approximately 2 percent of the genomes of European and Asian people today comes from Neanderthals.
Recent studies have shown that the alleles, or gene varieties, much of humanity inherited from this interaction are particularly associated with controlling the immune system. People with Neanderthal genetic inheritance are more likely to be resistant to certain diseases, providing an obvious evolutionary advantage. However, they are also more prone to allergies.
Dr Michael Dannemann and Dr Janet Kelso, from the Max Plank Institute for Evolutionary Anthropology, have extended this research using genetic data from 112,000 participants in the UK Biobank, which records DNA and aspects of physical appearance and behavior.
The researchers found that Neanderthal inheritance can have contrasting effects. While one Neanderthal allele is more common among people with blond hair, another is associated with darker coloring.
"These findings suggest that Neandertals might have differed in their hair and skin tones, much as people now do," Dannemann said in a statement. One Neanderthal allele is particularly rare among people with red hair.
More than half the common Neanderthal alleles identified influence coloring, but Neanderthal inheritance is more than skin deep. In The American Journal of Human Genetics, Dannemann and Kelso reveal that two Neanderthal alleles correlate with being an “evening person” – prone to late rising and falling asleep during the day.
"Skin and hair color, circadian rhythms and mood are all influenced by light exposure," the researchers wrote. Long occupation of high latitude environments that lack sunlight in winter could have driven the genetic changes.
The frequency of certain alleles indicates that the traits they produce were evolutionarily advantageous among modern humans, at least for those in certain regions. Most obviously, light skin allows people at northern latitudes to get plenty of vitamin D. Dannemann and Kelso think something similar applies to sleep patterns.
Perhaps harder to explain is the fact that one Neanderthal allele was associated with higher rates of smoking. However, Dannemann stressed to IFLScience that this does not mean Neanderthals were more prone to addictive behavior, as they may have had undiscovered alleles with the opposite effect.
The work coincides with the announcement of the second high-quality sequencing of a Neanderthal individual, which will increase the accuracy of future studies.